P. T. Guenther

Neutron total and scattering cross sections of some even Mo isotopes and the optical model

Abstract Neutron total cross sections of 92 Mo, 96 Mo, 98 Mo and 100 Mo were measured at intervals of ⪅ 10 keV from 1.6 to 5.5 MeV with resolutions of ≈ 10 keV. Neutron elastic and inelastic scattering cross sections of these isotopes were measured from 1.8 to 4.0 MeV at intervals of 0.2 MeV. Neutron groups corresponding to the excitation of forty states were identified. The experimental results were examined in the context of optical and statistical nuclear models. It was concluded that the real part of the optical potential includes a term proportional to [( N -Z)/ A ] and suggested that the imaginary part of the potential was shell dependent with decreasing magnitude as N = 50 is approached. Comparison of measured and calculated inelastic neutron excitation cross sections suggested a number of J π assignments extending previous knowledge.

The optical model of few-MeV neutron elastic scattering from Z = 39 to 51 targets

Abstract Neutron differential-elastic-scattering cross sections of elemental Y, Zr, Nb, Mo, Rh, Pd, Ag, Cd, In, Sn and Sb were measured from ≈ 1.5 to 4.0 MeV, at intervals of ≲ 100 keV, with resolutions of ≈ 50 to 75 keV, and at ten or more scattering angles distributed between 20 and 160°. Complementary broad-resolution neutron total cross sections of elemental Y, Nb Rh, Pd, In, Sn and Sb were measured from ≈ 0.8 to 4.5 MeV at intervals of ≲ 50 keV. The experimental results were interpreted within the framework of the spherical optical-statistical model (OM). A “regional” OM parameter set, quantitatively describing the neutron-nucleus interaction in this mass-energy domain, was deduced from the observed cross sections. Characteristics of this “regional” OM potential are discussed, particularly the geometric, isospin and shell-dependent properties.

Fast-neutron cross sections of the even isotopes of molybdenum

Abstract The neutron total and scattering cross sections of 92 Mo, 94 Mo, 96 Mo, 98 Mo and 100 Mo were experimentally determined. Total neutron cross sections were measured from 0.1 to 1.5 MeV. Neutron elastic and inelastic scattering cross sections were measured from 0.3 to 1.5 MeV. The excitation of states in 94 Mo at 879±10 keV, in 96 Mo at 786±10 and 1161±20 keV, in 98 Mo at 743±10 and 795±10 keV, and in 100 Mo at 520±20, 700±10, 1070±20 and 1147±20 keV was observed. The experimental results were interpreted in the context of the optical-statistical model concepts inclusive of resonance width fluctuation, direct excitation, and isotopie-dependent potential effects and statistically assayed for evidence of intermediate resonance structure.

Neutron emission from the 9Be(d, n)10B thick-target reaction for 7 MeV deuterons☆

Abstract Double-differential measurements of neutron emission from a thick beryllium target bombarded with 7 MeV deuterons are made for neutrons ≳ 0.8 MeV over the angular range 0–155°. The angular dependence of the neutron yield is found to be quite anisotropic. The importance of this anisotropy in integral neutron-induced reaction cross-section investigations is illustrated.

Energy dependence of the optical model potential for fast neutron scattering from cobalt

Abstract Differential elastic- and inelastic-scattering cross sections were measured from ∼ 1.5 to 10.0 MeV over the scattering-angle range ∼18° to 160°, with sufficient detail to define the energy-averaged behavior. Inelastic neutron groups were observed corresponding to measured excitation energies of: 1115 ± 29, 1212 ± 24, 1307 ± 24, 1503 ± 33, 1778 ± 40, 2112 ± 40, 2224 ± 35, 2423 ± 39, 2593 ± 41 and 2810 ± 67 keV. The experimental results were interpreted in terms of spherical-optical-statistical and coupled-channels models. A successful description of the differential elastic scattering below 10 MeV and the total cross section in the range 0–20 MeV was achieved using the spherical optical model with energy-dependent strengths and geometries. These energy dependencies are large below approximately 7.0 MeV, but become smaller and similar to those reported for “global” potentials at higher energies. This change in the energy dependence of the parameters, which occurs about 19 MeV above the Fermi energy, was also seen in the analysis of the 209 Bi data and probably marks the onset of the Fermi surface anomaly. Inelastic scattering to the levels below 1.8 MeV displays a forward peaked behavior. This non-statistical component is interpreted using the weak coupling model in which the f 7 2 proton hole is coupled to the 2 + state in 60 Ni. This vibrational characteristic provides an explanation of the unusual energy dependence and relatively small radius found for the imaginary optical model potential. In conjunction with the fact that cobalt is four neutrons away from the N = 28 closed shell, the coupling also provides an explanation for the large value of this potential. The real spherical optical-model potential derived from the neutron-scattering results was extrapolated to bound energies using the dispersion relationship and the method of moments. The resulting real-potential strength and radius peak at ∼ −10.0 MeV, whereas the real diffuseness is at a minimum at this energy. The extrapolated potential is ∼8% larger than that implied by reported particle-state energies, and ∼13% smaller than indicated by hole-state energies.

Neutron scattering and the fermi surface anomaly in 51V

Abstract Differential neutron elastic- and inelastic-scattering cross sections of vanadium were measured from 4.5 to 10.0 MeV. These results were combined with previous 1.5 to 4.0 MeV scattering data from this laboratory, the 11.1 MeV elastic-scattering results obtained at Ohio University, and the reported neutron total cross sections to energies of ∼ 20 MeV, to form a data base which was interpreted in terms of the spherical optical-statistical model. A fit to the data was achieved by making both the strengths and geometries of the optical-model potential energy dependent. These energy dependencies were large below ∼ 6 MeV, but were smaller, and similar to those characteristic of global models, at higher energies. Using the dispersion relationship and the method of moments, the optical-model potential deduced from the 0 to 11.1 MeV neutron scattering data was extrapolated to higher energies and to the bound-state regime. This extrapolation led to predicted neutron total cross sections that are in good agreement with experimental values to at least 20 MeV. For negative energies the values of the volume-integral per nucleon of the real potential are in excellent agreement with those needed to reproduce the observed binding energies of particle and hole states and give clear evidence of the Fermi surface anomaly. It is argued that the use of a global optical model for interpreting low-energy data is suspect but is probably a reasonable approximation at higher energies.

Neutron total, scattering and inelastic Gamma-ray cross sections of yttrium at few MeV energies

Neutron total, scattering and (n; n′,γ) cross sections of elemental yttrium (89Y) were measured in the few-MeV region. The neutron total-cross-section measurements were made with broad resolutions from ≈0.5 to 4.2MeV in steps of ≲0.1 MeV. Neutron elastic- and inelastic-scattering cross sections were measured from ≈1.5 to 4.0 MeV, at incident-neutron energy intervals of ≈50keV and at ten or more scattering angles distributed between 20 and 160 degrees using neutron detection. Inelastic-scattering cross sections were also determined using the (n; n′,γ) reaction at incident energies from 1.6 to 3.8 MeV at intervals of 0.1 MeV. Gamma-rays and/or inelastically-scattered neutrons were observed corresponding to the excitation of levels at: 909.0±0.5, 1,507.4 ±0.3, 1,744.5±0.3, 2,222.6±0.5, 2,530±0.8, 2,566.4±1.0, 2,622.5±1.0, 2,871.9 ±1.5, 2,880.6±2.0, 3,067.0±2.0, 3,107.0±2.0, 3,140.0±2.0, 3,410.0±2.0, 3,450.0±2.0, 3,504.0 ±1.5, 3,514.0±2.0, 3,556.0±2.0, 3,619.0±3.0, 3,629.0±3.0 and 3,715.0±3.0 keV. The experimental results are discussed in terms of the spherical-optical-statistical, coupledchannels, and core-coupling models, and in the context of previously reported excitedlevel structure.

Neutron total and scattering cross sections of 6Li in the low-MeV range☆

Abstract Neutron total cross sections of 6Li are measured at intervals of ≲ 10 keV from ≈ 0.1 to 4.8 MeV with precisions of ≈ 1 to 3 %. Differential elastic scattering cross sections are measured at intervals of ≲ 100 keV from 1.5 to 4.0 MeV at 10 or more scattering angles distributed between ≈ 20 and 160 deg. Differential inelastic scattering cross sections are measured at selected angles in the energy range 3.5 to 4.0 MeV. The experimental results are analyzed in terms of R-matrix theory and the model parameters used to deduce the 6 Li(n ,α) cross sections. The implications of the measurements and their interpretation on the level structure of 7Li and the reaction mechanisms are discussed.

The Interaction of Fast Neutrons with Nickel-60

Neutron total cross sections of /sup 60/Ni were measured with broad resolution from approx. 0.5 to 5.0 MeV at intervals of less than or equal to 50 keV. Differential elastic neutron scattering cross sections were measured from 1.5 to 4.0 MeV at intervals of less than or equal to 50 keV over the scattered neutron angular range from approx. 20 to 160/sup 0/. Differential cross sections for the inelastic neutron excitation of states at 1.342 +- 0.013, 2.168 +- 0.012, 2.304 +- 0.026, 2.509 +- 0.022, 2.636 +- 0.019, and 3.164 +- 0.041 MeV were also measured. The experimental results are interpreted in terms of optical-statistical and coupled-channel models, including consideration of compound nucleus fluctuations and direct-vibrational processes.

Total, scattering and γ-ray-production cross sections for few-MeV neutrons on 54Fe

Abstract Cross sections for the following neutron interactions were obtained for 54 Fe in the few-MeV incident-energy range with resolutions of 50–100 keV: total interaction from ∼0.5 to 4 MeV, elastic scattering from 1.2 to 4 MeV, inelastic scattering from 2 to 4 MeV for excitation energies up to 3 MeV, and inelastic-scattering γ-ray production from 1.4 to 3.6 MeV for transitions corresponding to the deexcitation of levels up to 3 MeV. The results are mutually consistent within experimental errors. A spherical optical-statistical model describes the energy-averaged behavior of these experiments reasonably well, although slight evidence for direct-reaction strength is exhibited by the angular distributions of neutrons scattered to the 1.408 MeV, 2 + , level.